Stochastic pump of interacting particles

We consider the overdamped motion of Brownian particles, interacting via particle exclusion, in an external potential that varies with time and space. We show that periodic potentials that maintain specific position-dependent phase relations generate time-averaged directed current of particles. We obtain analytic results for a lattice version of the model using a recently developed perturbative approach. Many interesting features like particle-hole symmetry, current reversal with changing density, and system-size dependence of current are obtained. We propose possible experiments to test our predictions.Comment: 4 pages, 2 figure

Prevalencia Estimada De Trastornos Conductuales Y Emocionales En La Población Pediátrica En Panamá

Objetivo. Estimar la prevalencia de trastornos conductuales y emocionales en una muestra de niños de edad escolar de la ciudad de Panamá mediante un estudio transversal realizado en el año escolar 2009. Métodos. Se obtuvo una muestra al azar de estudiantes de ambos sexos entre las edades de 6 y 11 años del sector este de la Región Metropolitana de Educación. Se utilizó un instrumento de evaluación estandarizado (BASC) diseñado para facilitar el diagnóstico de la clasificación pedagógica de una variedad de trastornos. La escala evalúa diversos aspectos de la conducta y la personalidad de los niños relacionados con los criterios diagnósticos de categorías de psicopatología del Manual Diagnóstico y Estadístico de los Trastornos Mentales (DSM-IV). La escala se aplica mediante cuestionarios suministrados a padres y maestros. Resultados. Un total de 131 díadas de padres y maestros fueron incluidas en los análisis. La prevalencia global estimada fue de 8.1%. El análisis de los trastornos individuales indicó que las condiciones más prevalentes fueron los problemas de aprendizaje (20.6%), las habilidades de estudio (26.0%) y la ansiedad (15.3%) según los maestros. Según los padres, las condiciones más prevalentes fueron el aislamiento (10.7%), la ansiedad (8.4%) y la falta de liderazgo (6.9%). Menos de uno en diez de los niños con un trastorno tuvo contacto con servicios de salud mental. Conclusiones. Este estudio es el primero que intenta estimar la prevalencia de trastornos psiquiátricos en la población pediátrica en Panamá. Los datos del estudio muestran una prevalencia de trastornos dentro del límite inferior a las cifras reportadas en estudios previos realizados en Latinoamérica. Sin embargo, un número considerable de niños mostró problemas de ansiedad y escolares, lo que destaca la importancia de evaluar las necesidades en salud mental en poblaciones pediátricas en estudios posteriores.Objetivo. Estimar la prevalencia de trastornos conductuales y emocionales en una muestra de niños de edad escolar de la ciudad de Panamá mediante un estudio transversal realizado en el año escolar 2009. Métodos. Se obtuvo una muestra al azar de estudiantes de ambos sexos entre las edades de 6 y 11 años del sector este de la Región Metropolitana de Educación. Se utilizó un instrumento de evaluación estandarizado (BASC) diseñado para facilitar el diagnóstico de la clasificación pedagógica de una variedad de trastornos. La escala evalúa diversos aspectos de la conducta y la personalidad de los niños relacionados con los criterios diagnósticos de categorías de psicopatología del Manual Diagnóstico y Estadístico de los Trastornos Mentales (DSM-IV). La escala se aplica mediante cuestionarios suministrados a padres y maestros. Resultados. Un total de 131 díadas de padres y maestros fueron incluidas en los análisis. La prevalencia global estimada fue de 8.1%. El análisis de los trastornos individuales indicó que las condiciones más prevalentes fueron los problemas de aprendizaje (20.6%), las habilidades de estudio (26.0%) y la ansiedad (15.3%) según los maestros. Según los padres, las condiciones más prevalentes fueron el aislamiento (10.7%), la ansiedad (8.4%) y la falta de liderazgo (6.9%). Menos de uno en diez de los niños con un trastorno tuvo contacto con servicios de salud mental. Conclusiones. Este estudio es el primero que intenta estimar la prevalencia de trastornos psiquiátricos en la población pediátrica en Panamá. Los datos del estudio muestran una prevalencia de trastornos dentro del límite inferior a las cifras reportadas en estudios previos realizados en Latinoamérica. Sin embargo, un número considerable de niños mostró problemas de ansiedad y escolares, lo que destaca la importancia de evaluar las necesidades en salud mental en poblaciones pediátricas en estudios posteriores

The (234)U neutron capture cross section measurement at the n_TOF facility

The neutron capture cross-section of (234)U has been measured for energies from thermal up to the keV region in the neutron time-of-flight facility n_TOF, based on a spallation source located at CERN. A 4 pi BaF(2) array composed of 40 crystals, placed at a distance of 184.9 m from the neutron source, was employed as a total absorption calorimeter (TAC) for detection of the prompt gamma-ray cascade from capture events in the sample. This text describes the experimental setup, all necessary steps followed during the data analysis procedure. Results are presented in the form of R-matrix resonance parameters from fits with the SAMMY code and compared to the evaluated data of ENDF in the relevant energy region, indicating the good performance of the n_TOF facility and the TAC

Measurements of high-energy neutron-induced fission of (nat)Pb and (209)Bi

This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly citedThe CERN Neutron Time-Of-Flight (n_TOF) facility is well suited to measure low cross sections as those of neutron-induced fission in subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors and a fragment coincidence method that allows us to identify the fission events. The present experiment provides first results for neutron-induced fission up to 1 GeV. Good agreement is found with previous experimental data below 200 MeV. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross sections is close to 1 GeV

Measurement of the (90,91,92,93,94,96)Zr(n,gamma) and (139)La(n,gamma) cross sections at n_TOF

Open AccessNeutron capture cross sections of Zr and La isotopes have important implications in the field of nuclear astrophysics as well as in the nuclear technology. In particular the Zr isotopes play a key role for the determination of the neutron density in the He burning zone of the Red Giant star, while the (139)La is important to monitor the s-process abundances from Ba up to Ph. Zr is also largely used as structural materials of traditional and advanced nuclear reactors. The nuclear resonance parameters and the cross section of (90,91,92,93,94,96)Zr and (139)La have been measured at the n_TOF facility at CERN. Based on these data the capture resonance strength and the Maxwellian-averaged cross section were calculated

New measurement of neutron capture resonances of 209Bi

The neutron capture cross section of Bi209 has been measured at the CERN n TOF facility by employing the pulse-height-weighting technique. Improvements over previous measurements are mainly because of an optimized detection system, which led to a practically negligible neutron sensitivity. Additional experimental sources of systematic error, such as the electronic threshold in the detectors, summing of gamma-rays, internal electron conversion, and the isomeric state in bismuth, have been taken into account. Gamma-ray absorption effects inside the sample have been corrected by employing a nonpolynomial weighting function. Because Bi209 is the last stable isotope in the reaction path of the stellar s-process, the Maxwellian averaged capture cross section is important for the recycling of the reaction flow by alpha-decays. In the relevant stellar range of thermal energies between kT=5 and 8 keV our new capture rate is about 16% higher than the presently accepted value used for nucleosynthesis calculations. At this low temperature an important part of the heavy Pb-Bi isotopes are supposed to be synthesized by the s-process in the He shells of low mass, thermally pulsing asymptotic giant branch stars. With the improved set of cross sections we obtain an s-process fraction of 19(3)% of the solar bismuth abundance, resulting in an r-process residual of 81(3)%. The present (n,gamma) cross-section measurement is also of relevance for the design of accelerator driven systems based on a liquid metal Pb/Bi spallation target.Comment: 10 pages, 5figures, recently published in Phys. Rev.

Evaluación del Sargazo (Sargassum spp.) como componente de sustratos agrícolas

Sargassum (Sargassum spp.) is a brown macroalga with anomalous arrivals on Caribbean beaches during the last decade, generating a problem for local tourism due to its unappealing look and smell when decomposing along the coast. To provide different management options, research studies have proposed incorporating it into different industrial processes ranging from cosmetics, construction and food production. The latter includes treatments leading to its physicochemical conditioning and subsequent use as an agricultural substrate, however, research on its performance is scarce. Therefore, this study aims to determine the physical and chemical characteristics of a sample of algae collected in Puerto Progreso, Yucatan, México, as well as their effect on the germination of two horticultural species. The results were compared with the characteristics and performance of peat (Peat moss®) and showed unfavourable physical properties when used as a single component, as well as high concentration of heavy metals, sodium and calcium ions that would limit its use in the food industry, in addition to negatively interfering with the germination stages. Therefore, it is suggested to test mixtures of sargassum with other materials that allow for improving its physical characteristics while buffering metal concentrations, in addition to devising mechanisms to reduce their concentration or completely eliminate them from the substrate.El sargazo (Sargassum spp.) es una macroalga parda que durante la última década ha presentado arribos anómalos en playas caribeñas, generando una problemática al turismo local por el aspecto y olor que adquiere cundo se descompone sobre el litoral. Para dar alternativas de manejo algunas investigaciones han propuesto incorporarlo a diferentes procesos industriales que van desde la cosmética, la construcción y la producción de alimentos. Dentro este último, se han reportado tratamientos para su acondicionamiento físico-químico y posterior uso como sustrato agrícola, sin embargo, las investigaciones de su desempeño son escasas. Por ello en el presente trabajo se determinaron las características físicas y químicas de una muestra del alga colectada en Puerto Progreso, Yucatán, México, así como las implicaciones de estas sobre la germinación de dos especies hortícolas. Las determinaciones fueron comparadas con las características y desempeño de turba (Sphagnum spp. Comercialmente llamado Peat moss®). Los resultados mostraron propiedades físicas desfavorables cuando se usa como componente único, así como una alta concentración de plomo (Pb), ion sodio y calcio que limitan su uso en la industria alimenticia, además de que interfieren negativamente con las etapas de germinación. Debido a esto, se recomienda probar mezclas de sargazo con otros materiales que permitan mejorar sus características físicas, así como amortiguar las concentraciones de metales, además de idear mecanismos para reducir su concentración o eliminarlos completamente del sustrato

Measurement of the neutron capture cross section of the s-only isotope 204Pb from 1 eV to 440 keV

The neutron capture cross section of 204Pb has been measured at the CERN n_TOF installation with high resolution in the energy range from 1 eV to 440 keV. An R-matrix analysis of the resolved resonance region, between 1 eV and 100 keV, was carried out using the SAMMY code. In the interval between 100 keV and 440 keV we report the average capture cross section. The background in the entire neutron energy range could be reliably determined from the measurement of a 208Pb sample. Other systematic effects in this measurement could be investigated and precisely corrected by means of detailed Monte Carlo simulations. We obtain a Maxwellian average capture cross section for 204Pb at kT=30 keV of 79(3) mb, in agreement with previous experiments. However our cross section at kT=5 keV is about 35% larger than the values reported so far. The implications of the new cross section for the s-process abundance contributions in the Pb/Bi region are discussed.Comment: 8 pages, 3 figures, article submitted to Phys. Rev.

Measurement of the radiative neutron capture cross section of 206Pb and its astrophysical implications

The (n, gamma) cross section of 206Pb has been measured at the CERN n_TOF facility with high resolution in the energy range from 1 eV to 600 keV by using two optimized C6D6 detectors. In the investigated energy interval about 130 resonances could be observed, from which 61 had enough statistics to be reliably analyzed via the R-matrix analysis code SAMMY. Experimental uncertainties were minimized, in particular with respect to (i) angular distribution effects of the prompt capture gamma-rays, and to (ii) the TOF-dependent background due to sample-scattered neutrons. Other background components were addressed by background measurements with an enriched 208Pb sample. The effect of the lower energy cutoff in the pulse height spectra of the C6D6 detectors was carefully corrected via Monte Carlo simulations. Compared to previous 206Pb values, the Maxwellian averaged capture cross sections derived from these data are about 20% and 9% lower at thermal energies of 5 keV and 30 keV, respectively. These new results have a direct impact on the s-process abundance of 206Pb, which represents an important test for the interpretation of the cosmic clock based on the decay of 238U.Comment: 11 pages, 8 figures, paper to be submitted to Phys. Rev.

Application of Photon Strength Functions to (n,g ) Measurements with the n_TOF TAC

The neutron capture cross section measurements at the CERN n_TOF facility are performed using a new detection system, the segmented Total Absorption Calorimeter (TAC). All measurements are performed in reference to the well known 197Au s (n,g ). The accuracy of the measurements depends on the accuracy of the TAC detection efficiency, which is calculated by means of Monte Carlo simulations. In this MC simulation photon strength functions and level densities play a major role as ingredients used for the generation of primary events, that is the electromagnetic cascades following the (n,g ) process. We have calculated the TAC detection efficiency for the case of 197Au(n,g ) by adjusting the photon strength functions of 198Au so that the simulation reproduces the experimental data. Both the MC method and the uncertainty of the results are discussed.JRC.D.5-Neutron physic